U.S. Pat. No. 7,046,228 discloses an electrophoretic display device having a dual switching mode which allows the charged pigment particles in a display cell to move in either the vertical (up/down) direction or the planar (left/right) direction. In such a display device, each of the display cells is sandwiched between two layers, one of which comprises a transparent top electrode, whereas the other layer comprises a bottom electrode and at least one in-plane electrode. Typically, the display cells are filled with a clear, but colored dielectric solvent or solvent mixture with charged white pigment particles dispersed therein. The background color of the display cells may be black. When the charged pigment particles are driven to be at or near the transparent top electrode, the color of the particles is seen, from the top viewing side. When the charged pigment particles are driven to be at or near the bottom electrode, the color of the solvent is seen. When the charged pigment particles are driven to be at or near the in-plane electrode(s), the color of the display cell background is seen. Accordingly, each of the display cells is capable of displaying three color states, i.e., the color of the charged pigment particles, the color of the dielectric solvent or solvent mixture or the background color of the display cell. The dual mode electrophoretic display, according to the patent, may be driven by an active matrix system or by a passive matrix system.
When this dual mode scheme is used for a full color display application, each pixel will have three individual display cells that contain a white particle dispersion in a red, green or blue colored solvent, respectively, and each display cell must be aligned with a set of electrodes on a backplane. The alignment accuracy between the red/green/blue display cells and the electrodes on the backplane is important in order to achieve good color performance.
There are several US patent applications (US2009-0273827, US2009-0251763, US2010-0165448, US2010-0165005 and US2010-0053728) which disclose color display devices, in some of which the electrodes on the backplane may be aligned or un-aligned with the display cells.